The invention relates to a sliding bearing for engine applications, in particular, a sliding bearing shell for the mounting of the crankshaft or the camshaft or for use as a connecting-rod bearing shell, with a metallic supporting layer and, applied on top of that, a bearing metal layer of aluminum alloy, copper alloy, or brass.
It is already known that a thin run-in or emergency plastics-based layer can be applied to bearing metal layers for sliding bearings for engine applications, that is, a layer made of a matrix-forming binding agent and solid lubricants held therein that improve the sliding properties.
WO 2004/113749 A1 discloses and describes a matrix comprising modified epoxy resin, i.e. a mixture of epoxy resin and phenolic resin, or a polyimide-amide resin with a greater proportion of polyimide, the layer comprising 15 to 30% by volume of a metallic powder, 1 to 15% by volume of a fluoropolymer, 0.5 to 20% by volume of a ceramic powder, and 2 to 15% by volume of silica. PTFE is the fluoropolymer used by preference.
GB-A-2 384 033 also discloses a bearing shell for a piston cross-head bearing of a marine engine with an approximately 20-μm thick coating. The coating comprises a synthetic resin from the group polyamide-imide, polybenzimidazole, polyamide, epoxy or phenolic resin. As the solid lubricant, at least a component of the group PTFE, MoS2, graphite, boron nitride, polyethersulfon is stated. As hard particles, at least a substance from the group of metal oxides (such as TiO2, Al2O3, etc.), of carbides (such as WC, MO2C, SiC etc.), of nitrides (such as Si3N4 etc.) are stated.
Finally, metal powder such as Cu, Ag, Zn etc. is disclosed. Most of the examples with a PAI-based coating contain PTFE. A single PTFE-free PAI-based coating compound contains 40% by volume of MOS2 and 1% by volume of TiO2. A further PTFE-free variant is not PAI-based but PBI-based and contains 3% by volume of SiC and 40% by volume of graphite.
EP-A-0 984 182 discloses a sliding bearing for engine applications of the said type with a paint coating based on polyimide, polyamide-imide, epoxy or phenolic resin with 55 to 90% by weight of MOS2. A confusingly large quantity of further additives is also mentioned, including zinc sulfide. Its proportion is 0.5 to 10% by weight, but preferably only 1 to 5% by weight, and in total no more than 10% by weight. The particle size of the additives is <5 μm, in particular, <2 μm.
The object of this invention is to improve the run-in and emergency performance of sliding bearings for engine applications, particularly to improve the semi-fluid friction where conditions are regularly critical. Semi-fluid friction is a condition that can arise on starting or possibly (temporarily) under high loads during operation when the sliding elements are not separated by a continuous film of lubricant (hydrodynamic state). This condition particularly results in wear that reduces the service life of the sliding bearing. In the case of thin run-in and emergency layers especially, there is the problem of the adherence of the thin surface coating to the bearing metal layer, which is essential for the functioning of the sliding bearing.